1. Field of the Invention
The present invention relates to a magnetoresistive (MR) read transducer, such as a spin valve giant magnetoresistive (GMR) read transducer. In particular, the invention relates to a magnetoresistive read head comprising a magnetoresistive layer extending over a level plane, an end surface defined at the end of the magnetoresistive layer by a plane intersecting the level plane, and a hard magnetic bias layer formed along the end surface of the magnetoresistive layer, and to a method of producing the same.
2. Description of the Prior Art
A magnetic read head employing a so-called spin valve giant magnetoresistive (GMR) sensor often includes a pair of hard magnetic bias layers connected to opposite end surfaces or abutting junctions of the spin valve GMR sensor or layer. The hard magnetic bias layers serve to produce a bias so as to reliably unipolarize the free magnetic layer. Such unipolarization or generation of a single domain in the free magnetic layer allows less Barkhausen noise to appear in the output from the magnetic read head.
The end surface of the spin valve GMR sensor may be defined by an inclined plane so as to receive the hard magnetic bias layer with a larger contact area. The increased contact area between the spin valve GMR sensor and the hard magnetic bias layer serves to reduce the electric resistance induced between the spin valve GMR sensor and the hard magnetic bias layer.
In general, the tip end of the hard magnetic bias layer, extending along the inclined end surface, reaches or overlaps the top surface of the spin valve GMR sensor. The increased overlap amount over the top surface of the spin valve GMR sensor causes a larger Barkhausen noise as disclosed in Japanese Patent Laid-open No. 10-49832. However, it is nearly impossible to form the hard magnetic bias layers without allowing the hard magnetic bias layers to overlap over the top surface of the spin valve GMR sensor under the conventional process of producing the magnetic read head comprising a spin valve GMR sensor. It is required to reduce the Barkhausen noise while accepting a relatively larger overlap amount of the hard magnetic bias layer over the top surface of the spin valve GMR sensor.
It is accordingly an object of the present invention to provide a magnetoresistive read head capable of reducing the Barkhausen noise while accepting a relatively larger overlap amount of hard magnetic bias layers over the top surface of the spin valve GMR layer.
According to the present invention, there is provided a magnetoresistive read head comprising: a magnetoresistive layer extending over a level plane to include a free magnetic layer; an end surface defined at an end of the magnetoresistive layer by an inclined plane intersecting the level plane by an inclination angle larger than 40xc2x0 and a hard magnetic bias layer allowing its tip end to reach a top surface of the magnetoresistive layer, wherein an overlap amount measured from the tip end of the hard magnetic bias layer to a terminal end of the free magnetic layer is set smaller than 0.282 xcexcm.
The present inventors have found that Barkhausen noise appearing in the output from the magnetoresistive layer has a correlation to the overlap amount measured from the tip end of the hard magnetic bias layer to the terminal end of the free magnetic layer as a result of their unique observation. It has been confirmed that the magnitude of Barkhausen noise depends upon the overlap amount irrespective of the amount of the hard magnetic bias layer covering over the top surface of the magnetoresistive layer. Specifically, as long as the overlap amount is set smaller than 0.282 xcexcm in accordance with the present invention, Barkhausen noise can be suppressed to the utmost. The overlap amount smaller than 0.282 xcexcm accepts a larger inclination angle between the level plane and the end surface of the magnetoresistive layer. Larger inclination angle serves to achieve a larger amount of the hard magnetic bias layer covering over the top surface of the magnetoresistive layer.
In particular, the end surface of the magnetoresistive layer preferably intersects the level plane by the inclination angle larger than 40xc2x0. A larger inclination angle set in this manner serves to reliably accept a larger amount of the hard magnetic bias layer covering over the top surface of the magnetoresistive layer.
The magnetoresistive layer may comprise the free magnetic layer, a non-magnetic spacer layer, a pinned magnetic layer and an antiferromagnetic layer, laminated over the level surface in sequence. A multilayer structure of this type is in general called a spin valve GMR sensor, which provides a superior sensitivity irrespective of the velocity of the movement of the magnetic recording medium. The spin valve GMR sensor allows the domain of the pinned magnetic layer to be fixed at a predetermined direction under the influence of the antiferromagnetic layer. On the other hand, the domain of the free magnetic layer is adapted to rotate under the influence of the magnetic field from the magnetic recording medium. Such rotation of the domain serves to change the level of the electric resistance of the spin valve GMR sensor. The change in the electric resistance is utilized to detect the binary data on the magnetic recording medium. It should be noted that the pinned magnetic layer, the non-magnetic spacer layer and the free magnetic layer may be laminated upon the level plane in this sequence in the magnetoresistive layer.
The aforementioned magnetoresistive read head may further comprise a flying head slider exposing the magnetoresistive layer at a bottom surface. Employment of the flying head slider is well known in the field of magnetic disk drives such as a hard disk drive (HDD). However, the magnetoresistive read head may be mounted on a support body other than the flying head slider. In addition, the magnetoresistive read head is also applicable to any magnetic recording medium drive, such as a magnetic tape drive, other than the HDD. Any of the aforementioned magnetoresistive read head can be employed in combination with a write head such as a thin film magnetic head or inductive write head.
Fabrication of the aforementioned magnetoresistive read head may be achieved by a production method comprising: forming a magnetoresistive layer on the surface of a wafer; subjecting ion milling to the magnetoresistive layer with a mask disposed above the surface of the magnetoresistive layer by a predetermined height so as to define on the magnetoresistive layer an end surface intersecting the surface of the wafer; and subjecting sputtering to the surface of the wafer with a target disposed above the surface of the wafer by a predetermined height without removing the mask so as to form a hard magnetic bias layer allowing the tip end to reach the top surface of the magnetoresistive layer from the end surface. Suitable control to the inclination angle of the end surface and the height of the target allows an adjustment to the overlap amount. Control to the inclination angle can be achieved by controlling the height of the mask and the incidence of the ion beams in the ion milling.
In particular, it is preferable to form the magnetoresistive layer and the hard magnetic bias layer continuously in vacuum atmosphere. Continuous formation in vacuum atmosphere in this manner serves to avoid oxidation at the boundary between the magnetoresistive layer and the hard magnetic bias layer, so that it is possible to reduce the electric resistance between the magnetoresistive layer and the hard magnetic bias layer.
Moreover, an inclination angle larger than 40xc2x0 is preferably defined between the surface of the wafer and the end surface of the magnetoresistive layer in the ion milling. A larger inclination angle set in this manner serves to reliably accept a larger amount of the hard magnetic bias layer covering over the top surface of the magnetoresistive layer. Although a conventional method may be employed to fabricate the aforementioned magnetoresistive read head, Barkhausen noise is reliably suppressed to the utmost in the fabricated magnetoresistive read head.